The rate-limiting step in the enzymatic hydrolysis of lignocellulose is generally considered to be the breakdown of crystalline cellulose by cellobiohydrolases (CBHs). Among the non-complexed fungal cellulose systems, glycosyl hydrolase family 7 cellobiohydrolases are the most well studied glycosyl hydrolase enzymes and have dominated the industrial applications of cellulases. However, owing to their extremely slow rate of catalysis, industrial application of these enzymes would benefit greatly from improvements in their hydrolytic capabilities.